The present invention relates to the exposure of offset printing plates and more specifically to a storage device for storing unexposed plates and automatically loading them onto an exposure unit and for removing and discarding interleaf paper-sheets located between the unexposed plates.
A CTP system accepts input jobs/pages written in a page description language, for example, Postscript. The jobs are sent through a raster image processor to a platemaker for exposure. The platemaker engine images the raster data on a plate, which is later mounted on the press, inked and made ready for printing.
The inclusion of a CTP system into a printing operation suggests a greater extent of automation that can be achieved. A full CTP process can automate, through the use of computers and special equipment, the transfer of information from the original layout to the press plate.
Also included in the automation of a CTP system is the media handling. It is necessary to supply plates individually from a plate supply area to the platemaker engine and it is desirable to reduce the amount of operator handling involved. Unexposed plates are normally supplied in packages of 25 to 100 plates, with interleaf paper-sheets between the plates for protecting the emulsion side of the plates, which is extremely sensitive to scratches. The stack of plates needs to be loaded into a supply area of a platemaker in a manner that will keep the stack of plates aligned with automation mechanisms for removing a plate from the stack, and for discarding the interleaf sheets from the stack.
An existing CTP system, which is marketed under the LithoSetter mark by Barco Graphics, Belgium, contains a slip-sheet removal mechanism that utilizes suction cups on a picking bar to lift the leading edge of the slip-sheet so that a vacuum table may be moved underneath the slip-sheet. Once the slip-sheet is resting entirely on the vacuum table, suction is applied to adhere the slip-sheet to the vacuum table and the table then carries the slip-sheet to a discard area.
Another slip-sheet removal mechanism, implemented in the Trendsetter VLF CTP machine produced and sold by Creo Inc., Canada, utilizes suction applied through holes in two concentric cylinders, which are attached to a picking arm, in order to grasp the slip-sheet and carry it to two pinch-rollers that guide it into a discard bin.
U.S. Pat. No. 5,992,324 to Rombult et at describes an automatic plate loading system, including a plate handler in which plates are stored horizontally in equal-sized stacks and a slip-sheet removal mechanism. When the stack containing plates of the required size has been positioned in an access position inside the plate handler, a picking mechanism picks the topmost plate and transports it to the imaging area. Air flow is then activated to peel off an edge of the slip-sheet, followed by gripping the peeled-off edge by mechanical xe2x80x9cfingersxe2x80x9d and lowering the cassette to further separate the slip-sheet from the plate above. The slip-sheet is then sucked by suction-cups, to separate it from the plate underneath and is rotatably driven out of the cassette and released.
The Lotem CTP machine, produced and sold by Creo Inc., Canada, also includes a horizontal plate-storage in cassettes, wherein the cassettes move vertically and the active cassette slides out of the storage area and into the imaging area where a picker picks the topmost plate and subsequently the slip-sheet lying underneath the picked plate is removed.
The systems mentioned above use horizontal storage of the plates. There are some advantages to vertical storage, such as:
Transporting plates in a vertical position is more efficient, since the travel distance is shorter
Vertical handling of plates reduces the probability of one plate slipping against another and scratching it
Floor space may be more efficiently used, especially when very large plates are being used.
With imaging processes getting faster, due to technological improvements such as multi-beam imaging, it is foreseen that the process of plate loading will become a bottle-neck, unless made more efficient, for example by performing the plate picking and the slip-sheet removal in parallel.
An additional effect of the faster imaging will be a greater amount of discarded paper accumulating per unit of time.
There is thus a need for a fast and reliable process of plate loading and slip-sheet removal, in which the discarded paper occupies minimal volume.
It is an object of the present invention to supply two mechanisms for simultaneously removing a plate and an inter-plate paper sheet, so as to speed-up the plate loading process.
It is another object of the present invention to provide a new method and apparatus for storing unexposed plates in a plate supply area.
There is thus provided, according to one aspect of the present invention, a vertical storage and loading apparatus for sheet articles, comprising:
a storage carousel;
a picking mechanism for picking one of said sheet articles stored in said carousel,
wherein a plurality of said sheet articles are stored vertically in said carousel.
According to one embodiment of this aspect, the storage carousel comprises:
a base;
a rotating body; and
a plurality of sheet holder pairs, slidingly movable along at least one track, said at least one track on the upper surface of said base.
Accoding to another embodiment of this aspect, the carousel is round.
Accoding to another embodiment of this aspect, the picking mechanism is transportable between a picking position, for picking a sheet article from said carousel and a delivering position.
Accoding to another embodiment of this aspect, the picking mechanism comprises vacuum.
Accoding to another embodiment of this aspect, the apparatus additionally comprises loading means for loading said sheet articles onto said carousel.
Accoding to another embodiment of this aspect, the apparatus additionally comprises slip-sheet removal mechanism for removing protective slip-sheets positioned between said stored sheet articles.
The slip-sheet removal mechanism may comprise a friction wheel and may deposit the removed slip-sheets horizontaaly, preferrably within the base of the carousel.
Accoding to another embodiment of this aspect, the picking mechanism is transportable between a picking position, for picking a sheet article from said carousel and a delivering position.
Accoding to another embodiment of this aspect, the picking mechanism comprises vacuum.
Accoding to another embodiment of this aspect, the apparatus additionally comprises loading means for loading said sheet articles onto said carousel.
Accoding to another embodiment of this aspect, the apparatus additionally comprises slip-sheet removal mechanism for removing protective slip-sheets positioned between said stored sheet articles.
The slip-sheet removal mechanism may comprise a friction wheel and may deposit the slip-sheets horizontally, preferrably within said carousel base.
According to another aspect of the present invention, there is provided a vertical storage and loading apparatus for printing plates, In a Computer To Plate (CTP) system, comprising:
a storage carousel; and
a picking mechanism for picking one of said printing plates stored in said carousel,
wherein a plurality of said printing plates are stored vertically in said carousel.
According to another aspect of the present invention, there is provided a CTP system comprising:
an imaging device for imaging printing plates;
an imaging surface for holding said printing plates during said imaging; and
a vertical storage and loading apparatus comprising:
a storage carousel; and
a picking mechanism for picking one of said printing plates stored in said carousel,
wherein a plurality of said printing plates are stored vertically in said carousel.
The imaging surface may be an external drum, an internal drum or a flatbed. According to another aspect of the present invention, there is provided a method of storing and loading sheet articles, comprising the steps of:
providing a storage carousel for storing a plurality of said sheet articles;
providing a picking mechanism;
storing said sheet articles in said carousel in a vertical position; and
using said picking mechanism for picking one of said sheet articles and delivering said picked sheet article to a depositing location.
According to one embodiment of this aspect, the storage carousel comprises:
a base;
a rotating body; and
a plurality of sheet holder pairs, slidingly movable along at least one track, said at least one track on the upper surface of said base.
According to another embodiment of this aspect, the carousel is round.
According to another embodiment of this aspect, the picking mechanism comprises vacuum.
According to another embodiment of this aspect, the method additionally comprising the step of removing protective slip-sheets positioned between said stored sheet articles.
The step of removing said protective slip-sheets may comprise using a friction wheel.
The slip-sheets may be deposited horizontally, preferrably within said carousel base.
In another aspect of the present invention there is a method of storing and loading printing plates provided in a Computer To Plate (CTP) system, comprising the steps of:
providing a storage carousel for storing a plurality of said printing plates;
providing a picking mechanism;
storing said printing plates in said carousel in a vertical position; and
using said picking mechanism for picking one of said stored plates and delivering said picked plate to an imaging surface.
The imaging surface may be an external drum, an internal drum, or a flatbed.